


Predilection

by Raikishi



Category: Fire Emblem: Fuukasetsugetsu | Fire Emblem: Three Houses
Genre: Asexuality Spectrum, Communication, Developing Relationship, Explicit Sexual Content, M/M, Male My Unit | Byleth, Multi, Public Sex, Relationship Negotiation, Threesome - M/M/M
Language: English
Status: Completed
Published: 2020-11-04
Updated: 2020-11-04
Packaged: 2021-03-09 03:35:46
Rating: Mature
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 3,554
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/27388054
Author URL: https://archiveofourown.org/users/Raikishi/pseuds/Raikishi
Summary: The thing is Felix knows Sylvain is a slut. It’s not like Sylvain bothers to hide it. He’s brazenly proud of the fact. Like it’s a damn skill that he greets folks with his cock instead of a handshake.To their utter shock, Byleth is a bit of a hussy too.In which Felix has a different sex drive compared to his partners and has to work out the words to convey that.Polyweek Day 2: Communication/Sleeping arrangement
Relationships: Felix Hugo Fraldarius/My Unit | Byleth, Felix Hugo Fraldarius/Sylvain Jose Gautier, Felix Hugo Fraldarius/Sylvain Jose Gautier/My Unit | Byleth, Sylvain Jose Gautier/My Unit | Byleth
Comments: 6
Kudos: 68





	Predilection

**Author's Note:**

> I wasn't planning on participating in poly week but I needed a distraction for election night. Turns out working out pronouns and limbs and grammar helps, but also makes you want to die. 
> 
> I'm gonna go drink now. Or write Dimitri getting his back blown out by Dedue and Byleth for one of the other prompts. 
> 
> Wish me luck.

The thing is Felix knows Sylvain is a slut. It’s not like Sylvain bothers to hide it. He’s brazenly proud of the fact. Like it’s a damn skill that he greets folks with his cock instead of a handshake. Felix had expected those urges to cool down after the night in Fhirdiad, when the three of them – Felix, Sylvain, and their once Professor – had stumbled, wine-drunk and buzzing on thank-the-Goddess-we’re-alive adrenaline, into one of the many closets in Fhirdiad castle. 

_“Fuck, that’s enough sex to last a lifetime,”_ Sylvain had declared to the ceiling, wide-eyed with shocked delight, as deliriously happy as he’d been when he’d managed a trot on a stallion.  


A part of Felix had been relieved. It had been good sex. He’d cum at least twice and he had had a nice ache and soreness on his body that typically came from training. But he’d not felt an enormous urge to leap into it again. Not anytime soon. He could not imagine keeping the sort of pace Sylvain had – Sylvain had never been without a person in his bed, before or during the war. So when Sylvain had declared that after their first night, Felix had latched onto it like a promise. One that gets broken within hours. 

Because, as it turns out, it’s not enough sex to last a lifetime. 

Not for Sylvain. And not for Byleth. To their utter shock, Byleth is a bit of a hussy too.

Felix hadn’t expected it. Neither had Sylvain.

The first time Byleth shoves his hand down Sylvain’s pants in public is only hours after their own private victory celebration in Fhirdiad. 

Sylvain had shrieked. It’d been terrible. The knights, battle-ready and war-forged, had rushed to their aid and a furiously red-faced Sylvain – so he did know shame – had weakly explained to them all that he’d just had a little too much drink and thought he’d seen a mouse. 

It’s only when the knights shuffle away that Felix notices Byleth’s hand in the back of Sylvain’s pants instead of the front, working steadily in rhythmic motions that had the redhead blushing like a virgin bride, hands twisting helplessly in the blue cloak he wears around his waist, struggling desperately to hide his shame –

A fluke, Felix thinks at first.

Byleth’s a teasing bastard sometimes. And Felix can appreciate Sylvain being on the receiving end of a vicious tease. He had amused himself with the desperately pleading looks and whispered whines Sylvain had cast over his shoulders until Byleth had been persuaded to stop. It’s funny. A joke.

Because Byleth is stoic, serene, and a demon on the battleground. Byleth hadn’t gone out in search of any warm body to share his bed in their academy days or even during the war. 

Byleth, Felix had assumed, was like him.

* * *

He couldn’t have been more wrong. 

“Heya, Professor, what’re you thinking just staring off into the distance? With that backdrop, you look like you’re waiting for a dashing knight to come sweep you away, may I–“

“I was thinking I’d like to spread your legs over the railing and fuck you right here for anyone to see.”

Sylvain chokes on nothing. So does Felix.

Byleth seems to take that to mean he’s insulted them both because he looks between the two of them, a touch apologetic, hunching his shoulders, “Either of you – you know I don’t prefer one to the other and I like you both equal–“

“Oh, yeah?” Sylvain husks out, the first to recover. His voice cracks over his next words. Obviously thinking with his cock again. Felix glowers at the twitch in Sylvain's trousers as if it’d personally offended him, “Tell me about it, Professor.”

Apparently that’s all the encouragement Byleth needs. He licks his palm and shoves his hand down the front of Sylvain’s pants. Hooks two fingers against his bottom teeth as if reigning in an animal. There’s a beatific smile on Byleth’s face, too sweet for the words that next come out of his mouth. 

“Maybe if you’re a good boy you can fuck Felix’s mouth as I take you from behind,” Byleth muses, his hand jerking Sylvain slow and steady. The cavalier shudders, full-bodied, “Or I can have you suck us off right here and leave you twitching and desperate to be enjoyed –“

“I’ll go keep watch,” Felix says, his head spinning with the brazen declaration, “If you’re going to make fools of yourself. At least you won’t be caught –“

He ignores the call to come back. He doesn’t want to be a part of it. He can’t do that. Can’t just –

He stands rigid and immoveable at the end of the hall, glaring down anyone who dared step close to him, entire body buzzing with a faint discomfort. 

They reappear thirty minutes later. Byleth has a post-sex look, Felix realizes, lax and sleepy-eyed like a cat in sunshine. The urge to pet twitches his fingers but he can smell spend and sex and – 

He wrinkles his nose at the dribble of cum on Sylvain’s jaw.

Felix spits at him to clean up, something burning in his chest when Sylvain chuckles and nudges Byleth slyly for being a cruel taskmaster, and maybe next time he can stand to be a bit gentler, hm? 

And apparently Byleth had been cruel. There’s finger point bruises on Sylvain’s hips and a score of mottled bites at the base of Sylvain’s throat. 

“Still plenty of space to add your own,” Sylvain winks at Felix. 

And Felix –

He smothers a retort, buzzing with … something, and pretends he does not hear what they're asking.  


* * *

It keeps happening. 

Byleth and Sylvain are insatiable. That first time opens floodgates Felix hadn't been expecting.  


“Oh, Goddess!” Dimitri shrieks, voice shrill. He stumbles backward out of the stables, one hand over his eye. A red blush spreads over his cheeks, ears, and neck, “I-I beg your pardon, P-Professor. I didn’t – I did not mean to intrude – oh, _Goddess_ – my sincerest apologies – I didn’t –“

“ _You_ don’t have to apologize,” Felix corrects him, kicking at Dimitri’s calf. He levels a glower at Byleth – _who still hasn’t taken his mouth off Sylvain’s cock_ – and Sylvain, “Oy, get the hell out you fucking animals.”

“O-okay, yeah, sure – sorry Your Hig – _ngh!_ – Your Majesty – _shit,_ Byleth, c’mon, you’ve gotta –“

“Come back in five,” Byleth pops his mouth off Sylvain’s cock and they all choke as he fists his hand over the crown, ears burning at the filthy slick sound as Byleth strokes from root to tip. He levels a stare at them that is not at _all_ suitable for someone caught in flagrante delicto – as if _they_ were the ones in the wrong – “He’s so close.”

“Goddess – _Byleth –_ “

“Y-yes, Professor! We’re leaving!” Dimitri jumps to obey, no doubt reacting to the whip crack of authority in their former Professor’s voice. He grimaces over Sylvain’s choked gasp, looking as if he’s seconds from taking out his other eye and maybe his ears as well, before slamming the door closed on –

“You can leave Felix –“

But Felix seizes Dimitri by the arm, wheeling them both far away from the stables. 

“Ah … um … shall we walk instead?” Dimitri asks loudly, eyes round. No doubt he’d caught the strains of the final order even over the slam of the stable doors.

“If you mention any of this, I’m going to stab you.”

“Felix,” Dimitri says grimly, “If I ever think of this moment again, I _want_ you to stab me.”

“...Deal.”

Felix can't help his snarl when Byleth and Sylvain turn up five minutes later – Byleth is as punctual as always. There's hay sticking in Sylvain’s hair and telltale rumples in his shirt. They could’ve at least made an attempt to clean up, Felix notes, trying to work out the uncomfortable block in his throat. It's irritation. Has to be. He certainly has a right to be irked when his ~~lovers~~ Byleth–and–Sylvain have been ogled by people that are not him. 

He’s fine. It’s a normal irritation. 

It’s –

* * *

The next week is full of Felix catching them in various states of undress around the castle.

“What’re you thinking, Byleth?” has turned into Sylvain’s favorite game. 

And it always leads to them falling into some form of annoyingly athletic sex – where the hell was Sylvain’s flexibility and strength when they were sparring? Fucking nowhere. Maybe he has a quota of flexibility and he wastes it on getting his dick wet. 

Felix glowers at the way Sylvain’s curled up against Byleth, long limbs tucked small as he’s bounced up and down on Byleth’s cock. Glares harder at the easy flex and pull of Byleth’s biceps and the rhythmic snap of his hips. Felix could’ve done with a spar against that strength today. 

Distantly, Felix can understand the appeal of Sylvain’s body. The man’s built like a broadsword. Sturdily built. Long limbs. Needing two hands to command – two hands Byleth’s more than willing to lend given the grip he has on Sylvain’s ass – Goddess damned could they not control themselves for more than a few minutes – 

“H-hey, Felix,” Sylvain stutters and then buries his face in Byleth’s neck, shuddering as he grips his own cock.

“Hands off,” Byleth snaps and Sylvain obeys with a breathless chuckle, instead, sinking his nails into Byleth’s shoulders. 

They make no move to stop. Sylvain angles a salacious come-hither-look and Felix – 

Felix doesn’t know what he wants.

He slaps Sylvain’s ass with his scabbard, startling when it makes Sylvain’s entire body seize up, his ears burning with the wild moan that Sylvain lets out.

“O-ow, oh fuck– there’s a - that’s, _wow_ , – do it again, Felix,” Sylvain chuckles breathlessly, entire body shivering as he wraps his arms around Byleth's shoulders – and yeah, he’s definitely cumming or at least trying to –

“Claude’s coming for a visit. Dimitri wants you both with him – clean up,” Felix spits out at them both, tucking his sword tight against his side, pretending valiantly he is not sputtering and uncomfortable. 

Byleth blinks at him, pausing in his ministrations to level a too knowing stare – he’d always been too observant as their Professor. 

“Felix, are you –“

Felix doesn’t hear the rest of it. He’s turning on his heels and is striding away, his steps loud enough to drown out the question. 

* * *

The thing is, he’s not quite sure what his problem is. He’s not jealous. 

It’s fine that they enjoy each other. He’s relieved that they’ve fallen into each other so readily, knowing that it was a relationship difficult to build.

_“You were a spoiled brat who should pay for that Crest. Maybe I'll collect the debt.”_

– had made Byleth withdraw into himself. The words had haunted Sylvain in the years following Byleth’s fall. There’d been a series of near deaths, idiotic rescues that’d nearly lost Felix both of them, and a fresh scar stretching down Sylvain’s back before they’d fallen together at Fhirdiad castle.

No, Felix decides as he watches Sylvain guide Byleth down from a horse with a careful hand on Byleth’s back and his face pressed to Byleth’s chest, Felix is not jealous in the least. 

There’s nothing but warmth in his chest at the sight and a deep pleasure that makes him shiver but then –

Sylvain’s hands squeeze Byleth’s ass and there’s no one else around so of course, Byleth’s going to swallow down Sylvain’s tongue. Of course, Byleth’s going to grind back against Sylvain’s hips. Of course, Byleth’s going to drop to his knees –

Felix hisses when expectant teal eyes meet his, pushing away from the balcony railing to join Dimitri’s conversation, “Sure, I’ll go with you.”

“Thank you, Felix, I must admit, having you with me … takes a weight from my shoulders,” Dimitri says, rubbing at the back of his neck, “Blaiddyd and Fraldarius at Duscar again … ah, no, I won’t allow for any morbid thoughts, not when we are so close to peace.”

He smiles affectionately at Dedue, who pretends he hadn’t just been squeezing His Majesty’s hand, before turning back to Felix, “But will the Professor and Sylvain not miss your company?”

They won’t. They have each other. And it wasn’t as if he could do what they wanted of him if he stayed – 

“No.”

* * *

He’s proven distinctly wrong on the night of his return. 

Both Sylvain and Byleth are in his bed. For once they’re not fucking.

“Heya Felix,” Sylvain approaches difficult problems as he always has, with a little smile and carefully crafted cheer. 

In sharp contrast, Byleth is furious. Burning like the sun. The anger makes Felix’s pulse trip a little. They all forget sometimes that Byleth’s crafted like a hunting sword. Fair and delicate at the hilt. Serrated and sharp-edged everywhere else. Felix had never known what it was like to be on the receiving end of that blade. 

“I didn't realize you would be gone for a week,” Byleth says. He must be truly mad. He talks slower when he is, as if each word needed to be carefully selected. He’s wearing the same expression on his face he had when he’d killed Randolph to save him from a boar.

“Didn’t think you’d miss me –“

“We did," spoken in a low snarl.  


“Oh come on, Felix, we thought we were clear this was going to be the three of us after that night in Fhirdiad,” Sylvain translates, struggling to keep his words without judgment.

Felix bristles despite the effort.

“You don’t need me here to get your cock sucked –”

He curses when Byleth grabs him, swearing fitfully as his back bounces against the bed. He kicks up instinctively but Byleth pins him with as much ease as he does on the training grounds.

“Get off –“

“Was that what this was?” Byleth asks over his demand, his voice a harsh rasp, sharp with displeasure, “Just a quick tryst and nothing more?”

_“No_ ,” refuses to leave Felix’s mouth.

“You know we want you for more than just sex, right Felix?” Sylvain says in a low voice, quietly spoken as if he were trying to calm a spooked horse, “…I – I noticed you don’t like it much.”

Felix startles at the assessment, entire body drawing tight. He’s filled with a sharp urge to run.

“I like it fine.”

Sylvain gives him a soft look, so tender Felix could choke on it.

“Do you?” Byleth asks.

“Unless that was someone else’s cock you were choking on in that closet in Fhirdiad,” Felix spits, kicking futilely beneath Byleth.

Byleth’s expression twitches. The anger bleeds out of him. After a long moment, he sighs. 

“Well, I never choked.”

No, cause he has no damn gag reflex, the fucking cock-slut. Felix’s cheeks heat. He kicks out again, more half-hearted, “Dammit, lemme up.”

He’s surprised when Byleth acquiesces.

“Don’t run again,” Byleth warns. The same Professor voice he’d used when coaching Felix through those humiliating dance lessons for the White Heron Ball. 

“I never run.”

They’re gracious enough to not refute him.

“I want you to tell us,” Byleth says, one hand curled loosely around Felix’s ankle, “What exactly you want.”

“… I like sex fine,” Felix says reflexively.

He’d been more than comfortable curled up in the dead center of their own private victory celebration. Had tolerated the disgusting mess left over and greatly preferred the after when Byleth had spent long moments cleaning him up and Sylvain had pressed delighted kisses down his back. Liked it even better when he’d been wrapped up in Byleth’s cloak, back linked up against Sylvain’s broad chest, his fingers knotted in Byleth’s hair.

That had also been different. Felix had gone in search. Had expected it. He’d not simply been tossed in headfirst and _dammit,_ he shouldn’t have to explain this –

“Felix,” Byleth’s lips brush carefully against his forehead, chaste and soft. Felix leans into it, “We cannot read your mind.” And then after a pause, “Linhardt’s still trying to figure out the magic for that – life would be so much easier if I could simply think and people would know, Professor – but I have no desire in making you uncomfortable for another decade before he manages to get something to work.”

Decade.

That sounds nice.

Felix feels a blush creeping over his cheeks at the not-quite promise, faintly relieved when he sees the same on Sylvain’s face. 

“I like sex fine,” he says again, grateful that they say nothing about how he’d been repeating himself like a fool. It makes the next words easier, “I just don’t want it as often as you do. I’d be fine if we just sparred. Or if we fucked once a moon. Or if we never fucked. I just – I don’t –“

“You don’t need it,” Sylvain observes.

Felix bobs his head.

“You know that’s fine,” Byleth states.

“…Yes.”

A raised eyebrow. A faint glimmer of disbelief. 

“I know it’s fine,” he says slowly, a weight loosening from his shoulders when Byleth squeezes his hand and Sylvain takes the other. 

“Are you uncomfortable seeing us fuck?” Byleth asks. 

“Yes. No,” Felix tries out both answers, squirming out of his skin trying to fit a correct one to Byleth’s question, “Maybe. I don’t know.”

“We can do it elsewhere, away from –“

As if Felix wants them hiding away from him like a dirty secret. No. Felix wants them in his bed. In his space. Wants to wake up to them tucked against his back and chest, sleep-addled and soft and –

He grabs for Byleth’s thigh, squeezing hard, “Don’t want you hiding away to do it – I don’t –“

“Want to feel like you’re being left out,” Sylvain observes.

Felix lets out a slow breath of relief. 

“Maybe you _can_ read minds,” Byleth says, faintly impressed. 

He rubs Sylvain’s face as if he were petting one of the monastery cats. Sylvain leans into it just as the cats do, with a pleased little smile and a flutter to his lashes. Felix reaches out to scratch his nails through Sylvain’s hair. His pulse flutters when Sylvain brushes a kiss to the underside of his wrist and that – stuff like that Felix doesn’t mind being sprung on him. Would welcome kisses and Byleth’s warmth against his chest. Sylvain’s calloused fingers carding through his hair –

“You can fuck in front of me,” he decides and then wrinkles his nose, “Not in front of anyone else though, you fucking degenerates. But don’t ask me to join. Don’t go expecting it. I’d prefer if you didn’t ask or just – I mean –“

“Ah,” Byleth breaths out, visible distress making his expression fall. He leans in close, “We never intended to make you feel _obliged_ to participate. Felix, I didn’t go chasing after you in Fhirdiad because I wanted a fuck. I sought you out – _both_ of you because the war is over as are my duties and maybe, just maybe, I’d like to chase after a future _I_ desire instead of someone else’s dreams.” 

Oh – 

Felix feels his heart skip. He looks away, unable to meet the intensity of Byleth’s gaze. Sylvain’s expression is much the same.

“If you recall, I said, if we're together, I don't even care if I stay locked up inside for the rest of my life,” Sylvain reminds him, “If you told me you didn't want me to look at another person, I'd go blind if you insisted –“

“I know –“ Felix cuts him off. It’d been embarrassing to hear the first time. It’s embarrassing now. 

“I don't need to fuck you against a wall daily,” Byleth continues needlessly, rolling his eyes, “I’d be happy if I look to my side and see you both there.”

Felix husks out a sharp breath, relief spilling over his chest, bright and warm, a rush of emotion that makes him weak.

“Oh. Ok,” he manages and then clears his throat, “Somedays I might still want but … if I do– if I want, I’ll – “

“You’ll be the one to let us know,” Byleth says firmly, “In the meantime, you must know we do not expect your participation as some sort of obligation you must fulfill to keep us together.”

“Right,” Felix swallows. 

“We will not do anything that makes you uncomfortable,” Byleth says.

An iron declaration. But then again, Byleth had always been that way.

_“We will_ ** _not_** _march on Enbarr.”_

And just like that, they hadn’t.

“Okay,” Felix says quietly, shuffling so as to tuck himself between them, his ankles looping around Byleth’s and his head against Sylvain’s chest. 

“That wasn’t so hard, now was it Felix?” Sylvain asks after a long moment.

“Better than war,” Felix mutters grimly.

“Wow, we’re honored.”

“It was certainly easier than coaxing words out of Dimitri when he was –“

Felix kicks at Byleth, “Don’t mention another man in my bed.”

“I don’t think he’s going to be coming near us any time soon,” Sylvain chuckles - shameless.

“Mmm, do you have regrets?” Byleth asks, reaching out with pinching fingers to tweak at Sylvain’s nipples. 

Felix kicks at both of them, _“Sleep_ tonight, you animals. You can fuck in the morning.”

“Hmm,” Sylvain hums and the noise is thick with a plot but he’s tucked up chaste and obedient against Felix’s back and is a comfortable pillow to Felix’s head so Felix offers no complaints. At least not tonight –

* * *

He saves them for the next morning when he wakes up to the bed beating against the wall. 

**Author's Note:**

> Felix at 6 AM days later, stabbing the bed: I don't get no sleep cause of ya'll, ya'll not gon get no sleep cause of me


End file.
